This invention relates to a touch sensor, and more specifically, to enhancing contact or pressure between a mold closure and a workpiece to prevent lateral movement of the workpiece during compression molding.
Typically, a multilayered workpiece is formed layer by layer, where individual layers can vary by at least 5-10% in thickness. The workpiece is then debulked by applying a vacuum and heat to remove gas and pre-densify the workpiece. Finally, the workpiece is placed in a sealed bag in a mold and further densified into a final formed workpiece using only autoclave air pressure. Compression molding a debulked workpiece, however, has been found to provide better exterior surface geometry than conventional autoclave molding, as well as forcing the workpiece to a final geometry which is less dependent on material layer variability.
In a compression molding process, the preformed workpiece is assembled similar to the autoclave process. Instead of autoclave molding the workpiece for final densification, however, the debulked workpiece is placed in a compression mold cavity and a mold closure moves into contact with the workpiece while the mold is also heated according to a pre-determined temperature schedule. Final densification of the workpiece is performed by compressing the workpiece between the mold cavity and the mold closure within the mold.
Unfortunately, the act of obtaining better exterior surface geometry through compression molding may, in some cases, lead to the generation of excessive lateral flow of one or more layers of the workpiece. The excessive lateral flow may tend to form wrinkles in the one or more layers. Such wrinkles create an abnormality in the workpiece and in some cases may lead to a derating of the strength of the final formed workpiece.
One cause for the excessive lateral flow is believed to be non-uniform contact between the mold and the workpiece, particularly upon initial contact of the mold with the workpiece before compression molding commences. Another cause is believed to be non-uniform pressure applied to the workpiece during compression molding. Consequently, it is desirable to assure that the mold contacts the preformed workpiece as completely and uniformly as possible before and during compression molding to reduce the likelihood of excessive lateral motion of the workpiece relative to the mold. For a similar reason, it is desirable to assure that the pressure applied upon the preformed workpiece during compression molding is tailored to get a high quality part.
Accordingly, there is a need in the art for an improved mold closure.